1. Field of the Invention
The invention relates to branched polysiloxane compositions of particular use as mist suppressants in silicone-based paper release coatings.
2. Description of the Prior Art
It is well known that in operations where silicone-based paper release coating formulations are subjected to a high enough rotational or translational motion, e.g., in high speed roll coating of flexible supports and paper, misting and/or aerosoling can become significant problems. These problems become particularly significant when applying these release coatings at roll coating speeds approaching 1000 ft/min, while the trend in the paper coating industry is to use speeds in excess of 1500 ft/min, e.g., 2000-3000 ft/min. In addition to having a deleterious effect on manufacturing operations, these mist and aerosol particles present industrial hygiene and safety issues for those people operating or working in the vicinity of the coating equipment.
Specialized chemical formulations known generically as “mist suppressants” have commonly been used to reduce the formation of mist in such operations. For example, U.S. Pat. Nos. 6,805,914 and 6,489,407 (hereinafter the '914 and '407 patents) disclose silicone mist suppressant compositions derived from reacting an excess of at least one organohydrogensilicone compound containing at least three silicon-bonded hydrogen groups per molecule (component (a)) with at least one compound containing at least two alkenyl groups per molecule (component (b)), wherein the ratio of the number of silicon-bonded hydrogen atoms of component (a) to the number of alkenyl groups of component (b) is at least 4.6:1, and more preferably from 4.6:1 to 500:1.
U.S. Pat. No. 6,586,535 discloses essentially the inverse of the '914 and '407 patents, i.e., silicone mist suppressant compositions derived from reacting at least one organohydrogensilicon compound containing at least two silicon-bonded hydrogen groups with an excess of at least one organoalkenylsiloxane compound containing at least three silicon-bonded alkenyl groups, wherein the ratio of the number of silicon-bonded hydrogen atoms of component (a) to the number of alkenyl groups of component (b) is less than or equal to 1:4.6, and preferably from 1:4.6 to 1:500.
U.S. Pat. Nos. 6,764,717 and 6,956,096 disclose silicone-based mist suppressant compositions derived from a two-step process involving: (a) reacting a hydrocarbon containing at least three aliphatic double bonds with a stoichiometric excess of organosiloxane compounds having terminal silicon-bonded hydrogen atoms, wherein the ratio of silicon-bonded hydrogen to aliphatic double bonds is from 1.3 to 10, and preferably from 1.5 to 5; and (b) reacting the resulting hydrocarbon-siloxane copolymers, which contain silicon-bonded hydrogen atoms, with a stoichiometric excess of α,ω-dialkenylsiloxane polymer, wherein the ratio of aliphatic double bonds in the α,ω-dialkenylsiloxane polymer to silicon-bonded hydrogen in the hydrocarbon-siloxane copolymer obtained in the first step is from 1.2 to 10, preferably from 1.5 to 5.0.
U.S. Pat. Nos. 6,887,949, 6,774,201, and 6,727,338 disclose silicone polymers as anti-mist additives wherein unsaturated hydrocarbon compounds are included in the synthesis of the silicone polymers.
U.S. Pat. No. 5,625,023 discloses mist suppressant compositions derived by reacting an organosilicon compound, an oxyalkylene-containing compound, and a catalyst.
U.S. Pat. No. 5,399,614 discloses adhesive compositions containing alkenyl-terminated polydiorganosiloxanes and silylhydride-terminated organohydrogenpolysiloxanes.
However, there remains a need for mist suppressant compositions which have at least the same or an improved capability of mist reduction while providing other benefits, such as cost savings, ease of production, ease of use, and/or broader application to a variety of end uses.